This training program focuses on developing and applying a laser microscopy technique to image pigmented lesions. The long-term objective is to fundamentally improve the detection and treatment of melanoma. Presently, melanoma is diagnosed from a pathologist's examination of a biopsy. While the criteria for evaluation were developed from the study of thick melanomas (with a typically fatal patient outcome), the majority of today's rising incidence of melanoma is accounted for by thin, early-stage lesions. Some pathologists question whether these criteria accurately predict a thin lesion's potential to develop into cancer. Furthermore, numerous studies have concluded that pathologists examining the same biopsy often disagree on the diagnosis of melanoma. Other studies have concluded that the rising incidence of melanoma can be explained by an 'epidemic' of overdiagnoses and costly false negatives. What is clear is that better methods are need for detecting melanoma and separating benign from malignant pigmented lesions. Therefore, there is a need for studies of early-stage melanoma, in order to look for biomarkers that reliably predict a suspicious lesion's malignant potential. This requires two things: a live model of early stage melanoma and an imaging method that is well suited for characterizing pigmented lesions. To this end, we propose in vivo imaging of an animal model (human skin, seeded with melanoma cell lines, grafted onto mice) with nonlinear pump-probe microscopy. Nonlinear pump-probe microscopy is a modality ideally suited for studying pigmented lesions. This method measures the microscopic distribution of the two types of melanin found in human skin, eumelanin and pheomelanin. The distribution of these pigments is of clinical importance: when compared with benign lesions, melanomas tend to contain more eumelanin and have a spatially heterogeneous pigment composition. This chemical contrast based on pump-probe spectroscopy of melanin reports on the metabolism and biologic behavior of melanocytes, the cells involved in melanoma. The pump-probe images are acquired noninvasively, without disrupting the skin under study, with considerably less optical intensity than is used in commercially available skin imaging systems based on multiphoton autofluorescence. The specific aims are: 1) to improve contrast between melanocytes and keratinocytes; 2) to image the different progressive stages of early melanoma; and 3) to investigate the feasibility of extending pump-probe microscopy to a related condition, ocular melanoma.